It has been conventional to pour liquid metal into parallel sided continuous casting molds for the production of steel ingots, billets and slab, while maintaining the conditions of pouring, cooling and withdrawal so that the still liquid metal core within the embryonic casting, extends down into and through the parallel walled zone at the distal end of the mold (e.g. DE PS No. 887,990).
With the conventional equipments, the conclusion of casting is done by reducing both the pouring rate and the withdrawal rate, allowing for the removal of the scum (oxide) layer from the surface of the molten or liquid metal bath (which will be referred to herein simply as the "metal bath") and permitting the melt to develop a solidified covering layer as the casting is being withdrawn from the mold. With strip steel casting, however, in which a mold is used having a flared pouring zone such a procedure does not work because any bridging or solidification within the metal in the flared zone above the neck of the mold results in resistance which prevents the end of the casting from being withdrawn through the neck. For this reason, even in cases when the liquid core of the casting may still extend down into the parallel walled distal zone of the mold, unacceptible break-out causing bridging resistances are frequently experienced during the concluding phases of the casting of strip. This condition is, of course, brought on and exacerbated by the necking down of the mold and the narrow cross-section of the strip which limits access to the surface of the metal bath. The further consequence of this is that the scum or slag on the widened surface of the metal bath at the top of the flared zone is difficult to remove and tends to be carried further downstream where it can foul the guides, or if it is entrapped within the casting, it can cause surface blisters on a casting when such materials penetrate into the surface of the casting and thereafter the casting is subjected to the water sprays between the idler rollers in the guides downstream of the mold. As a result, conventionally, substantial inconvenience and losses of metal occur at the time of concluding operations of a given melt.
Accordingly, it is an object of the invention to provide an operationally safe method and apparatus for the conclusion of the casting of a given melt in a continuous casting strip mill, which process and apparatus avoid the loss of stock through break-outs caused by the formation of plugs or resistance bridges above the neck of a flared-type mold and which also provide for the effective reduction of the scum on the surface of the metal bath in a continuous casting mold for strip, so as to avoid fouling the guides with same or causing the formation of blisters on the surface of the casting when applying sprayed water thereto.